The invention relates generally to ground adapters for electrical cables, especially those used aboard marine vessels and platforms. In particular, the invention relates to embodiments for low-impedance designs of a cable shield ground adapter (CSGA).
The United States Navy currently employs two technologies to provide electromagnetic (EM) protection from coupling to topside (i.e., above-deck) cables; conduit which provides an overall EM shield to cables placed within the conduit, and shielded cables with CSGAs used as termination connectors. Both technologies are viable but components used are expensive and difficult to maintain. The proposed CSGA embodiments deal almost exclusively with shielded cables and conduits. These are not explicitly described herein with respect to further applications, although the technology could be applied to the conduit shell whether flexible or rigid.
Conventional CSGA designs have been proven to be effective at grounding cable shielding when properly installed, achieving grounding effectiveness measures that exceed 80 decibels (dB). The conventional designs are designed for use with swage tubes, also known as stuffing tubes. Glenair® Inc. of Glendale, Calif. provides the primary conventional design currently in use. The Glenair® configuration requires the installer to employ CSGA components designed for specific cable sizes and swage tube sizes. Failure to use the exact tube size leads to performance failure for the system. The Glenair® CSGA also requires the installer to remove and discard the gland nut typically supplied with the swage tube by the swage tube manufacturer.
Once installed, the system is not easily repaired. Repair of a failed adapter can be accomplished through one of two methods. The first method requires the disconnection of the shielded cable from the system interface connector through cutting or de-soldering, removal and replacement of the failed component, and replacement of the interface connector. The second method requires a CSGA called a “Split Connector” that represents a device used for in situ replacement of the failed CSGA.
The failed CSGA must be removed from the swage tube, and the split connector is installed in its place. The components from the failed connector are then taped to the upper part of the cable and remain in place for the life of the connector, or until the CSGA assembly is replaced during a refit. The Glenair® system uses an exterior weather proof boot to provide exterior weather protection, but lacks interior protection against water intrusion. Their catalog is available at http://www.glenair.com/catalogs/entire_catalog_shipboard.pdf for lists of parts. A 3:02-minute video presentation on “MIL-PRF-24758A Conduit Assembly and EMI Shield Termination Procedure” available at Glenair® at http://www.glenair.com/video/24758a_full_monty.htm and more generally in a 2:57-minute presentation as “MIL-PRF-24758A Shipboard Conduit Assembly” at http://www.youtube.com/watch?v=Abmj0IN_A40 (without audio). Airmar® Technology in Milford, N.H. also provides an installation guide in http://www.airmartechnology.com/uploads/installguide/17-423-01.pdf.
Another conventional CSGA design, SkinTop®, is available from LAPP Group Inc. of Florham Park, N.J. The SkinTop® design incorporates squared-off contact fingers, which in addition to forming an ohmic contact, also perform a cable centering function. Without the squaring off of the contact, the cable would tend to roll off center. The resultant structural loading imposes the requirement of stiffer materials and shorter finger lengths for the SkinTop® design. The smallest clamping cable diameter for the conventional SkinTop® design is 0.118 inch (″) with a maximum variation of cable diameter of approximately 0.512″ for their largest design.
Additionally, the conventional Skintop® requires the use of a machined cable gland assembly and is therefore not adaptable to variances in the inner diameter of the swage tube. This imposes limits in the design as to the exact size of the swage tube's inner diameter, the units of measure (metric or SAE) and thread type of swage tube. The SkinTop® design also requires the removal and subsequent disposal of the gland nut supplied with the swage tube by the manufacturer. The basic design of the SkinTop® system appears more robust than the Glenair® system. However once installed, the SkinTop® arrangement is not easily repaired. Repair of a failed adapter requires the disconnection of the shielded cable from the system interface connector through cutting or de-soldering, removal and replacement of the failed component, and replacement of the interface connector. The Skintop® system uses a gland washer to provide exterior weather protection, and a weather proof boot can be added to provide additional exterior weather protection. Interior protection against water intrusion is not provided.